The present invention relates to a laser beam head and, more particularly, to a rotary laser beam head suitable for use in welding of fine tubes at their peripheries to an end plate which, in combination with the tubes, constitutes a heat exchanger. The rotary laser beam head of the invention, however, can apply other purposes than the welding: namely, cutting, heat treatment, surface treatment of materials, and a light source for laser communication systems.
FIG. 1 annexed to this specification shows a conventional apparatus for a laser beam welding, which is shown in an article entitled "Welding With a High-Power CO.sub.2 Laser" published in Society of Automotive Engineers in 1974. This apparatus is designed to conduct a welding along a circular welding line. In this apparatus, the laser beam 1 introduced into a rotary head 2 is reflected at a right angle by a reflecting mirror 3 having a parabolic surface and is concentrated or focussed in the direction of penetration depth to the welding portion by means of a stationary reflecting mirror 4. For effecting the welding along a circular welding line, the rotary laser beam head 2 is rotated at its bearing portion 5 in the direction of arrow 7.
This known apparatus has a drawback that, since the distance between the axis of rotation and the focussing point of the focussed laser beam 1 cannot be decreased below the diameter of the laser beam 1 coming into the rotary laser beam head 2, it is not possible to conduct the peripheral welding of a tube having a diameter smaller than the diameter of the laser beam.